Detecting the impact of a missile on a target makes it possible to activate a lethal chain of the missile. To do this, it is necessary to know the precise moment of the impact of the front point of the missile on the target so as to be able to trigger the lethal chain at the optimum moment.
For this purpose, the missile must be provided with an impact detection device (or impact sensor) which meets very strict conditions. In particular:                the impact sensor must not be destroyed before it has sent the impact information to a system for triggering the warhead(s);        the probability of the impact sensor functioning correctly must be as high as possible;        the probability of a false alarm leading to the warhead being triggered at the wrong time must be as low as possible; and        the dating of the moment of the impact must be very precise.        
Generally, the impact sensor must also be configured so as to take into account the presence of a homing device in the front point of the missile. Most missiles having homing devices integrate sensors for detecting the target. These sensors can be proximity sensors (“proximity fuses”) when triggering the warhead close to the target is required.
When detecting the impact of the front point on the target is required, a device which is designed to detect the opening (rupture) of an electrical conductor loop is frequently used. However, the reliability of an electrical conductor loop of this type is not optimal. There is a risk that the electrical loop will close again, if only very briefly, during the shock. Furthermore, in some configurations, using an electrical device can pose problems in terms of safety with respect to the warhead, which can be arranged close by, making it necessary to put into place electromagnetic shielding (increasing the mass of the assembly).
To remedy some of these drawbacks, FR 2 549 595 discloses an impact sensor for a projectile which can come into contact with a target in any zone of a casing. The casing is limited to a nose covering a front portion of the structure of the projectile. The impact sensor comprises a dielectric optical waveguide which is rigidly connected to the casing in all the zones that may come into contact with the impact and which transmits a luminous flux from a transmitter to a receiver. The dielectric guide is formed by an optical fibre or by a bundle of optical fibres which are flexible enough to follow a winding path over the casing. The optical fibre is wound in a fixed-pitch or variable-pitch helix whilst being fixed outside or inside the nose.
However, this conventional impact sensor having a dielectric optical waveguide is not optimal. In particular, said sensor is difficult to fit, difficult to reproduce, and it is difficult to predict how it will rupture.